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84
Pla z_ uk et al.
ꢂ
with 4b (e.g., compare ‘‘cone angles’’ of PPh and PBu , 145 and 132 ,
3
3
[10]
respectively ). The use of an excess of NaH extends its reactive surface
and the presence of the crown ether facilitates the transport of the ions into
solutions. These two facts ensure efficient deprotonation of 4a under
employed reaction conditions.
[
6]
In conclusion, we have found that despite earlier statement 4b can be
used in Wittig extension of polyenals when an excess of NaH and a catalytic
amount of 18-crown-6 is used for generation of the corresponding
phosphorance. An advantage of 4a over 4b is its stability and commercial
availability (Aldrich).
EXPERIMENTAL
General Procedure
To a stirred, argon-flushed solution of aldehyde (1.2 mmol), 4a (1.0 g,
.4 mmol) and 18-crown-6 (c.a. 5 mg) in THF (15 mL), NaH (120 mg,
mmol) was added in one portion. After 2 h stirring at r.t. the same amount
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5
of NaH was added and the stirring was continued overnight. The reaction
mixture was quenched with water (Caution: exothermic reaction, external
cooling required), the extracted with ether (3 ꢃ 50mL). After evaporation
of ether, the residue was dissolved in the mixture of THF (50 mL) and
20% HCl (20mL), stirred 2 h at r.t., alkalized with 10% NaOH and
extracted with dichloromethane (5 ꢃ 50mL). Drying (Na SO ), solvent
2
4
removal and chromatography (SiO /chloroform) afforded the product.
2
Compounds 1a–g were identified by comparison with authentic sam-
[6,8,9] 1
ples.
H NMR (200 MHz, CDCl , d): Ia: 9.56 (d, 1H, J ¼ 8.0 Hz),
3
7
.41 (d, 2H, J ¼ 8.9 Hz), 7.26 (dd, 1H, J ¼ 15.0 Hz and J ¼ 10.2 Hz), 6.96
(
d, lH, J ¼ 15.2 Hz), 6.82 (dd, 1H, J ¼ 15.3 Hz and J ¼ 10.2 Hz), 6.69
(
d, 2H, J ¼ 8.8 Hz), 6.18 (dd, 1H, J ¼ 15.0 Hz and J ¼ 8.0 Hz), 3.03 (s, 6H).
Ib: 9.54 (d, 1H, J ¼ 8.1 Hz), 6.39–7.42 (m, 9H), 6.13 (dd, 1H, J ¼ 6.8 Hz,
J ¼ 8.2 Hz), 3.00 (s, 6H). Ic: 9.55 (d, J ¼ 8.0 Hz, 1H), 7.42 (d, J ¼ 15.6 Hz,
1
H), 6.34 (dd, J ¼ 15.6 Hz and J ¼ 8.0 Hz, 1H), 4.55 (s, 2H), 4.51 (s, 2H),
.16 (s, 5H). Id: 9.56 (d, J ¼ 8.0 Hz, 1H), 7.16 (dd, J ¼ 15.1 Hz and
4
J ¼ 11.2 Hz, 1H), 6.89 (d, J ¼ 15.2 Hz, 1H), 6.59 (dd, J ¼ 15.1 Hz and
J ¼ 10.9 Hz, 1H), 6.15 (dd, J ¼ 15.1 Hz and J ¼ 7.8 Hz, 1H), 4.49 (s, 2H),
4
.28 (s, 2H), 4.16 (s, 5H). Ie: 9.57 (d, J ¼ 8.1 Hz, 1H), 7.15 (dd, J ¼ 15.0 Hz
and J ¼ 11.0 Hz, 1H), 6.74 (dd, J ¼ 11.4 Hz and J ¼ 10.0 Hz, 1H), 6.64
d, J ¼ 9.9 Hz, 1H), 6.50 (dd, J ¼ 14.7 Hz and J ¼ 10.7 Hz, 1H), 6.41 (dd,
J ¼ 11.6 Hz and J ¼ 10.0 Hz, 1H), 6.17 (dd, J ¼ 15.2 Hz and J ¼ 8.2 Hz,
(